re = /^([^,]*),([^,]*),([^,]*),(.*)/m
str = 'StreetA @ StreetB,1 NameA,DirectionA,Lat,Long
StreetC @ StreetD,1 NameA,DirectionA,Lat,Long
StreetE @ StreetF,1 NameA,DirectionB,Lat,Long
StreetG @ StreetH,1 NameA,DirectionB,Lat,Long
StreetI @ StreetJ,2 NameB,DirectionC,Lat,Long
StreetK @ StreetL,2 NameB,DirectionC,Lat,Long
StreetM @ StreetN,2 NameB,DirectionD,Lat,Long
StreetO @ StreetP,2 NameB,DirectionD,Lat,Long'
subst = '$2 - $3=[[$1,[\\4]]]'
result = str.gsub(re, subst)
# Print the result of the substitution
puts result
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html